CN111077372B - Method and system for measuring harmonic impedance of alternating current-direct current power transmission system - Google Patents

Method and system for measuring harmonic impedance of alternating current-direct current power transmission system Download PDF

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CN111077372B
CN111077372B CN201911348869.4A CN201911348869A CN111077372B CN 111077372 B CN111077372 B CN 111077372B CN 201911348869 A CN201911348869 A CN 201911348869A CN 111077372 B CN111077372 B CN 111077372B
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harmonic impedance
impedance
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CN111077372A (en
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樊丽娟
王海军
杨光源
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Maintenance and Test Center of Extra High Voltage Power Transmission Co
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Abstract

The invention discloses a method and a system for measuring harmonic impedance of an alternating current and direct current power transmission system, wherein the method comprises the steps of S1, acquiring real-time data in an electric power SCADA (supervisory control and data acquisition) system to calculate a harmonic impedance value of a calculation element required by the alternating current and direct current power transmission system under the current operation condition; and S2, respectively calculating the harmonic impedance values of different observation nodes in the alternating current system and the direct current transmission system under different frequencies by adopting a conventional alternating current system harmonic impedance calculation method for the harmonic impedance values of the required calculation elements calculated in the step S1 under the current operation condition. According to the invention, the harmonic impedance values of each element under the current operation working condition are calculated by using the field real-time data, and then the harmonic impedance values of different observation nodes under different frequencies can be obtained by using the conventional alternating current system harmonic impedance calculation method, and the result is accurate and effective, so that the normal operation of a power transmission system is ensured.

Description

Method and system for measuring harmonic impedance of alternating current-direct current power transmission system
Technical Field
The invention relates to the technical field of electric power, in particular to a method and a system for measuring harmonic impedance of an alternating-current and direct-current power transmission system.
Background
The function of the harmonic impedance scanning technology of the AC/DC power transmission system is as follows:
(1) the boundary conditions of the access system of the high-voltage direct-current transmission engineering converter station are complex, the operation modes are various, the harmonic impedance equivalent parameters for designing the alternating-current filter are reasonably determined, and the reasonable configuration of the scheme of the alternating-current filter can be realized.
(2) The high-voltage direct-current transmission system is a strong nonlinear system due to the fact that the high-voltage direct-current transmission system comprises a large number of power electronic switches and complex control links. In an electric power system, various background harmonics and harmonic problems caused by system disturbance acting on a high-voltage direct-current transmission system influence the normal operation of the system and even cause serious consequences that the system is stably damaged. Therefore, determining the harmonic impedance of a high voltage direct current transmission system is the key to the study of the harmonic problem of a high voltage direct current system.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provides a method and a system for measuring harmonic impedance of an alternating-current and direct-current power transmission system so as to accurately and effectively measure the value of the harmonic impedance and ensure the normal operation of the power transmission system.
In order to achieve the purpose, the technical scheme of the invention is as follows:
in a first aspect, an embodiment of the present invention provides a method for measuring harmonic impedance of an ac/dc power transmission system, including:
s1, acquiring real-time data in the power SCADA to calculate a harmonic impedance value of a calculation element required by the AC/DC power transmission system under the current operation condition;
and S2, respectively calculating the harmonic impedance values of different observation nodes in the alternating current system and the direct current transmission system under different frequencies by adopting a conventional alternating current system harmonic impedance calculation method for the harmonic impedance values of the required calculation elements calculated in the step S1 under the current operation condition.
In a second aspect, an embodiment of the present invention provides an ac/dc power transmission system harmonic impedance measurement system, including:
the data collector is used for collecting and acquiring real-time data in the electric power SCADA;
the first data processor is used for receiving the real-time data transmitted by the data acquisition unit so as to calculate the harmonic impedance value of the element required by the alternating current-direct current power transmission system under the current operating condition;
and the second data processor is used for calculating the harmonic impedance values of different observation nodes in the alternating current system and the direct current transmission system under different frequencies respectively by adopting a conventional alternating current system harmonic impedance operation processing method for the harmonic impedance values of the required calculation element under the current operation working condition obtained by the operation of the first data processor.
Compared with the prior art, the invention has the beneficial effects that:
according to the harmonic impedance measuring method for the alternating current-direct current power transmission system, the harmonic impedance values of all elements under the current operation working condition are calculated by using the field real-time data, then the harmonic impedance values of different observation nodes under different frequencies can be obtained by using the conventional alternating current system harmonic impedance calculating method, the result is accurate and effective, and therefore the normal operation of the power transmission system is guaranteed.
The harmonic impedance measuring system of the ac/dc power transmission system provided by this embodiment first acquires real-time data in the power SCADA through the data acquisition device, then the first data processor calculates a harmonic impedance value of each element under the current operating condition by using the real-time data of the power SCADA, and finally the second data processor performs operation processing on the harmonic impedance value of the element to be calculated under the current operating condition by using a conventional ac system harmonic impedance operation processing method, so that harmonic impedance values of different observation nodes under different frequencies can be obtained, and the result is accurate and effective, thereby being beneficial to ensuring the normal operation of the power transmission system.
Drawings
Fig. 1 is a flowchart of a method for measuring harmonic impedance of an ac/dc power transmission system according to embodiment 1 of the present invention;
fig. 2 is a schematic composition diagram of a harmonic impedance measurement system of an ac/dc power transmission system according to embodiment 2 of the present invention;
in the figure: 201. a data acquisition unit; 202. a first data processor; 203. a second data processor.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings and detailed description.
Example (b):
referring to fig. 1, the method for measuring harmonic impedance of an ac/dc power transmission system according to this embodiment includes the following steps:
s1, acquiring real-time Data in an electric power SCADA (Supervisory Control And Data Acquisition And monitoring Control system) to calculate a harmonic impedance value of a calculation element required by the AC/DC power transmission system under the current operation condition; in the step, because the harmonic impedance value of each element under the current operation condition is calculated by using the electric power SCADA real-time data, the nonlinear harmonic impedance characteristic and the time-varying harmonic impedance characteristic of each element of the actual power grid system are considered, the variability of the operation mode of the actual power grid system after the fault is considered, and the influence of other primary and secondary equipment accessed in the actual power grid system on the harmonic impedance calculation is considered.
And S2, respectively calculating the harmonic impedance values of different observation nodes in the alternating current system and the direct current transmission system under different frequencies by adopting a conventional alternating current system harmonic impedance calculation method for the harmonic impedance values of the required calculation elements calculated in the step S1 under the current operation condition.
Therefore, the harmonic impedance measuring method for the alternating current/direct current power transmission system provided by the embodiment can calculate the harmonic impedance value of each element under the current operation condition by using the field real-time data, and then can obtain the harmonic impedance values of different observation nodes under different frequencies by using the conventional alternating current system harmonic impedance calculating method, and the result is accurate and effective, so that the normal operation of the power transmission system is favorably ensured.
Specifically, the step S1 includes:
s101, acquiring real-time data in an electric power SCADA (supervisory control and data acquisition), wherein the acquired data comprise voltage sampling values, current sampling values and system frequency (unit: Hz) of each node in the same time period of an actual power grid system;
s102, setting a value K, and satisfying: f ═ K Δ f (K ═ 1,2, 3.); in the formula, delta f is frequency resolution, and f is power grid system frequency;
s103, presetting the power grid system frequency as a rated value of 50Hz, and according to a DFT (discrete Fourier transform) algorithm principle, performing DFT operation on sampling data of K cycles to enable the frequency resolution delta f of a DFT result and the power grid frequency f to meet a relation f-K delta f (K-1, 2, 3.);
s104, intercepting system frequency data acquired in the first K50 Hz periods in the electric power SCADA real-time data, and calculating the average value of the intercepted system frequency data to serve as the actual frequency f of the power grid;
s105, intercepting voltage and current sampling value data of each node acquired in the first K (hz) periods in the electric power SCADA real-time data, namely the data of the first K/f seconds;
s106, setting a frequency calculation range [ fmin,fmax]According to the sampling theorem, the number N of sampling points per whole period is more than or equal to fmaxF, wherein fmin＝K1Δf(K1＝1,2,3...)，fmax＝K2Δf(K2＝1,2,3...)，fmax≥fmin；
S107, for the intercepted voltage and current sampling value data of each node, when the number of sampling points N is less than f in the whole periodmaxWhen the sampling value is in the first sampling range, performing secondary sampling by using an interpolation algorithm to obtain sampling value data meeting the requirements;
s108, calculating the intercepted or interpolated voltage and current sampling value data of each node to obtain a frequency calculation range [ fmin,fmax]Phasor value of inner frequency point
Figure BDA0002334150940000031
And
Figure BDA0002334150940000032
wherein
Figure BDA0002334150940000033
And
Figure BDA0002334150940000034
voltage phasor and current phasor for the nth node fk (Hz) component, andmin≤fk≤fmax；
s109, selecting a frequency calculation point fjs＝fminCalculating the elements to be calculated at fjsImpedance values of the frequency points;
s110, calculating point f of cyclic change frequencyjs＝fmin+ K Δ f (K ═ 1,2, 3.), and step S109 is performed once until fjs＝fmin+KΔf＞fmaxJumping out of the cycle; obtaining the frequency-impedance value of each element to be calculated;
and S111, dividing the alternating-current and direct-current power transmission system into an alternating-current power transmission system part and a direct-current power transmission system part by taking the converter as a boundary, and respectively participating in subsequent harmonic impedance calculation.
Through the steps, the harmonic impedance value of each required calculation element under the current operation condition can be accurately and effectively calculated.
Specifically, in this embodiment, the above elements required for calculation include: the power generation system comprises a generator, a transformer, a power transmission line, a load, a current converter, an alternating current filter and a direct current filter; and the transformer includes a double winding transformer and a triple winding transformer.
For the generator, the terminal voltage quantities of the points are calculated using the corresponding frequencies
Figure BDA0002334150940000035
Terminal current phasor
Figure BDA0002334150940000036
Calculating the generator is in fjsImpedance value of frequency point:
Figure BDA0002334150940000041
for a two-winding transformer, the high-side voltage phasor of a point is calculated by using the corresponding frequency
Figure BDA0002334150940000042
And current phasor
Figure BDA0002334150940000043
Low side voltage phasor
Figure BDA0002334150940000044
And current phasor
Figure BDA0002334150940000045
Calculating transformer in fjsImpedance value of frequency point:
Figure BDA0002334150940000046
wherein: k is the actual transformation ratio of the transformer,
Figure BDA0002334150940000047
for settling to the high-voltage side of the transformer, etcAn effective impedance;
for the three-winding transformer, the same processing mode as BPA is used, namely the three-winding transformer is firstly converted into two double-winding transformers; then, calculating to obtain harmonic impedance values of the two double-winding transformers by utilizing the method for calculating the harmonic impedance of the double-winding transformers;
for the transmission line, the I-side voltage phasor of the point is calculated by using the corresponding frequency
Figure BDA0002334150940000048
And current phasor
Figure BDA0002334150940000049
Voltage phasor at J side
Figure BDA00023341509400000410
And current phasor
Figure BDA00023341509400000411
Calculating the line at fjsImpedance value of frequency point:
Figure BDA00023341509400000412
for the load, calculating the voltage phasor of the load node of the point by using the corresponding frequency
Figure BDA00023341509400000413
And load current phasor
Figure BDA00023341509400000414
Calculation load at fjsImpedance value of frequency point:
Figure BDA00023341509400000415
for the converter, the harmonic impedance calculation is divided into an AC side equivalent impedance and a DC side equivalent impedance:
equivalent impedance calculation at AC side of converter: converter power grid side alternating bus voltage phasor using corresponding frequency calculation points
Figure BDA00023341509400000416
And the current phasor input to the inverter
Figure BDA00023341509400000417
Calculating the current converter at fjsEquivalent impedance on the ac side of the frequency point:
Figure BDA00023341509400000418
calculating equivalent impedance of a direct current side of the converter: converter valve side DC bus voltage phasor using corresponding frequency calculation points
Figure BDA00023341509400000419
And the current phasor input to the inverter
Figure BDA00023341509400000420
Calculating the current converter at fjsEquivalent impedance on the direct current side of the frequency point:
Figure BDA00023341509400000421
for the converter transformer, the method for calculating the harmonic impedance is the same as the method for calculating the harmonic impedance of the double-winding transformer;
the harmonic impedance calculation method for the ac filter and the dc filter is the same as the method for calculating the load harmonic impedance described above.
The conventional method for calculating the harmonic impedance of the ac system in step S2 includes:
s201, aiming at a certain frequency, establishing a node admittance matrix; aiming at a certain observation node, solving a node voltage equation by a unit current injection method to obtain a harmonic impedance value of the observation node under the frequency;
s202, repeatedly executing the step S201 to obtain harmonic impedance values of different observation nodes under different frequencies.
Preferably, in step S107, the interpolation algorithm includes: high-order interpolation algorithms such as 2-order Lagrange interpolation, two-point cubic Hermite interpolation, cubic spline interpolation and the like are adopted to reduce interpolation errors.
Example 2:
referring to fig. 2, the system for measuring harmonic impedance of an ac/dc power transmission system according to this embodiment includes:
the data acquisition unit 201 is used for acquiring and acquiring real-time data in the electric power SCADA; in this embodiment, the data acquisition unit may use an existing data capture tool, such as a silicon valley data tool growth io, and then directly capture relevant real-time data from the electric power SCADA; after the relevant data is captured, the relevant data is transmitted to the first data processor 202;
the first data processor 202 is configured to receive real-time data transmitted by the data collector, and calculate a harmonic impedance value of a calculation element required by the ac/dc power transmission system under a current operating condition; because the first data processor 202 calculates the harmonic impedance value of each element under the current operation condition by using the electric power SCADA real-time data, the nonlinear harmonic impedance characteristic and the time-varying harmonic impedance characteristic of each element of the actual power grid system are considered, the variability of the operation mode of the actual power grid system after the fault is considered, and the influence of other primary and secondary equipment accessed in the actual power grid system on the harmonic impedance calculation is considered.
And the second data processor 203 is configured to calculate harmonic impedance values of different observation nodes in the alternating current system and the direct current power transmission system at different frequencies by using a conventional alternating current system harmonic impedance operation processing method for the harmonic impedance values of the required calculation element calculated by the first data processor under the current operating condition.
Therefore, the harmonic impedance measuring system of the ac/dc power transmission system provided by this embodiment acquires and obtains real-time data in the electric power SCADA through the data acquisition device, then the first data processor calculates the harmonic impedance value of each element under the current operating condition by using the electric power SCADA real-time data, and finally the second data processor performs operation processing on the harmonic impedance value of the element to be calculated under the current operating condition by using the conventional ac system harmonic impedance operation processing method, so that the harmonic impedance values of different observation nodes under different frequencies can be obtained, and the result is accurate and effective, thereby being beneficial to ensuring the normal operation of the power transmission system.
The specific working principle of the data collector 201 in this embodiment corresponds to step S101 in embodiment 1, the operation processing procedure of the first data processor 602 corresponds to steps S102 to S111 in embodiment 1, and the operation processing procedure of the second data processor 603 corresponds to step S2 in embodiment 1, so that the working principle and the operation processing procedure of the data collector 601, the first data processor 602, and the second data processor 603 are not described in detail in this embodiment.
As a preferable preference of the user electricity consumption behavior prediction system in this embodiment, the system further includes a client, the client is configured to receive the harmonic impedance values of different observation nodes at different frequencies, which are calculated by the second data receiving processor 203, and the client may be a mobile phone, a computer, or a tablet computer, so that a worker can remotely and real-timely obtain a final result of the operation.
The above embodiments are only for illustrating the technical concept and features of the present invention, and the purpose thereof is to enable those skilled in the art to understand the contents of the present invention and implement the present invention accordingly, and not to limit the protection scope of the present invention accordingly. All equivalent changes or modifications made in accordance with the spirit of the present disclosure are intended to be covered by the scope of the present disclosure.

Claims (7)

1. A method for measuring harmonic impedance of an AC/DC power transmission system is characterized by comprising the following steps:
s1, acquiring real-time data in the power SCADA to calculate a harmonic impedance value of a calculation element required by the AC/DC power transmission system under the current operation condition;
s2, respectively calculating harmonic impedance values of different observation nodes in the alternating current system and the direct current transmission system under different frequencies by adopting a conventional alternating current system harmonic impedance calculation method for the harmonic impedance value of the required calculation element calculated in the step S1 under the current operation condition;
the step S1 includes:
s101, acquiring real-time data in an electric power SCADA (supervisory control and data acquisition), wherein the acquired data comprise voltage sampling values, current sampling values and system frequency of each node in the same time period of an actual power grid system;
s102, setting a value K, and satisfying: f is K Δ f; in the formula, delta f is frequency resolution, f is power grid system frequency, the unit is Hz, and K is a positive integer;
s103, presetting the power grid system frequency as a rated value of 50Hz, and performing DFT operation on sampling value data of K cycles when the frequency resolution delta f of a DFT result and the power grid frequency f meet a relation f of K delta f according to the DFT algorithm principle;
s104, intercepting system frequency data acquired in the first K50 Hz periods in the electric power SCADA real-time data, and calculating the average value of the intercepted system frequency data to serve as the actual frequency f of the power grid;
s105, intercepting voltage and current sampling value data of each node acquired in the first K f periods in the electric power SCADA real-time data, namely the data of the first K/f seconds;
s106, setting a frequency calculation range [ fmin,fmax]And satisfies that the number of sampling points N per whole period is more than or equal to fmaxF, wherein fmin＝K1Δf，fmax＝K2Δf，fmax≥fmin，K1、K2Are all positive integers;
s107, for the intercepted voltage and current sampling value data of each node, when the number of sampling points N is less than f in the whole periodmaxWhen the sampling value is in the first sampling range, performing secondary sampling by using an interpolation algorithm to obtain sampling value data meeting the requirements;
s108, calculating the intercepted or interpolated voltage and current sampling value data of each node to obtain a frequency calculation range [ fmin,fmax]Phasor value of inner frequency point
Figure FDA0002669445720000011
And
Figure FDA0002669445720000012
wherein
Figure FDA0002669445720000013
And
Figure FDA0002669445720000014
is the n-th node fkVoltage phasor and current phasor of the components, and fmin≤fk≤fmax；fkThe unit is Hz;
s109, selecting a frequency calculation point fjs＝fminCalculating the elements to be calculated at fjsImpedance values of the frequency points;
s110, calculating point f of cyclic change frequencyjs＝fmin+ K Δ f (K ═ 1,2, 3.), and step S109 is performed once until fjs＝fmin+KΔf＞fmaxJumping out of the cycle; obtaining the frequency-impedance value of each element to be calculated;
and S111, dividing the alternating-current and direct-current power transmission system into an alternating-current power transmission system part and a direct-current power transmission system part by taking the converter as a boundary, and respectively participating in subsequent harmonic impedance calculation.
2. The method of measuring harmonic impedance of a ac/dc power transmission system of claim 1, wherein the elements to be calculated include: generator, transformer, transmission line, load, transverter, AC filter, direct current filter.
3. The method of harmonic impedance measurement in an ac/dc power transmission system of claim 2 wherein the transformers include a two-winding transformer and a three-winding transformer;
for the generator, the terminal voltage quantities of the points are calculated using the corresponding frequencies
Figure FDA0002669445720000021
Terminal current phasor
Figure FDA0002669445720000022
Calculating the generator is in fjsImpedance value of frequency point:
Figure FDA0002669445720000023
for a two-winding transformer, the high-side voltage phasor of a point is calculated by using the corresponding frequency
Figure FDA0002669445720000024
And current phasor
Figure FDA0002669445720000025
Low side voltage phasor
Figure FDA0002669445720000026
And current phasor
Figure FDA0002669445720000027
Calculating transformer in fjsImpedance value of frequency point:
Figure FDA0002669445720000028
wherein: k is the actual transformation ratio of the transformer,
Figure FDA0002669445720000029
to the equivalent impedance to the high voltage side of the transformer;
for the three-winding transformer, the same processing mode as BPA is used, namely the three-winding transformer is firstly converted into two double-winding transformers; then, calculating to obtain harmonic impedance values of the two double-winding transformers by utilizing the method for calculating the harmonic impedance of the double-winding transformers;
for transmission lines, correspondences are usedI-side voltage phasor of frequency calculation point
Figure FDA00026694457200000210
And current phasor
Figure FDA00026694457200000211
Voltage phasor at J side
Figure FDA00026694457200000212
And current phasor
Figure FDA00026694457200000213
Calculating the line at fjsImpedance value of frequency point:
Figure FDA00026694457200000214
for the load, calculating the voltage phasor of the load node of the point by using the corresponding frequency
Figure FDA00026694457200000215
And load current phasor
Figure FDA00026694457200000216
Calculation load at fjsImpedance value of frequency point:
Figure FDA00026694457200000217
for the converter, the harmonic impedance calculation is divided into an AC side equivalent impedance and a DC side equivalent impedance:
calculating equivalent impedance of the AC side of the converter: converter power grid side alternating bus voltage phasor using corresponding frequency calculation points
Figure FDA00026694457200000218
And the current phasor input to the inverter
Figure FDA00026694457200000219
Calculating the current converter at fjsEquivalent impedance on the ac side of the frequency point:
Figure FDA00026694457200000220
calculating equivalent impedance of a direct current side of the converter: converter valve side DC bus voltage phasor using corresponding frequency calculation points
Figure FDA00026694457200000221
And the current phasor input to the inverter
Figure FDA00026694457200000222
Calculating the current converter at fjsEquivalent impedance on the direct current side of the frequency point:
Figure FDA0002669445720000031
for the converter transformer, the method for calculating the harmonic impedance is the same as the method for calculating the harmonic impedance of the double-winding transformer;
the harmonic impedance calculation method for the ac filter and the dc filter is the same as the method for calculating the load harmonic impedance described above.
4. A method of measuring harmonic impedance of an ac/dc transmission system according to any of claims 2 to 3, wherein the conventional method of calculating harmonic impedance of an ac system in step S2 includes:
s201, aiming at a certain frequency, establishing a node admittance matrix; aiming at a certain observation node, solving a node voltage equation by a unit current injection method to obtain a harmonic impedance value of the observation node under the frequency;
s202, repeatedly executing the step S201 to obtain harmonic impedance values of different observation nodes under different frequencies.
5. The method of determining harmonic impedance of a ac/dc power transmission system of claim 1 wherein in step S107, the interpolation algorithm comprises: 2-order Lagrange interpolation, two-point cubic Hermite interpolation and cubic spline interpolation.
6. An alternating current-direct current transmission system harmonic impedance measuring system is characterized by comprising:
the data collector is used for collecting and acquiring real-time data in the electric power SCADA;
the first data processor is used for receiving the real-time data transmitted by the data acquisition unit so as to calculate the harmonic impedance value of the element required by the alternating current-direct current power transmission system under the current operating condition;
the second data processor is used for calculating harmonic impedance values of different observation nodes in the alternating current system and the direct current transmission system under different frequencies respectively by adopting a conventional alternating current system harmonic impedance operation processing method for the harmonic impedance values of the required calculation element under the current operation working condition obtained by the operation of the first data processor;
the real-time data collected by the data collector comprises: voltage sampling values, current sampling values and system frequency of each node in the same time period of the actual power grid system;
the calculation processing process of calculating the harmonic impedance value of the calculation element required by the alternating current and direct current power transmission system under the current operation condition by the first data processor is as follows:
s102, setting a value K, and satisfying: f is K Δ f; in the formula, delta f is frequency resolution, f is power grid system frequency, and K is a positive integer;
s103, presetting the power grid system frequency as a rated value of 50Hz, and performing DFT operation on sampling value data of K cycles when the frequency resolution delta f of a DFT result and the power grid frequency f meet a relation f of K delta f according to the DFT algorithm principle;
s104, intercepting system frequency data acquired in the first K50 Hz periods in the electric power SCADA real-time data, and calculating the average value of the intercepted system frequency data to serve as the actual frequency f of the power grid;
s105, intercepting voltage and current sampling value data of each node acquired in the first K f periods in the electric power SCADA real-time data, namely the data of the first K/f seconds;
s106, setting a frequency calculation range [ fmin,fmax]And satisfies that the number of sampling points N per whole period is more than or equal to fmaxF, wherein fmin＝K1Δf，fmax＝K2Δf，fmax≥fmin；K1、K2Are all positive integers;
s107, for the intercepted voltage and current sampling value data of each node, when the number of sampling points N is less than f in the whole periodmaxWhen the sampling value is in the first sampling range, performing secondary sampling by using an interpolation algorithm to obtain sampling value data meeting the requirements;
s108, calculating the intercepted or interpolated voltage and current sampling value data of each node to obtain a frequency calculation range [ fmin,fmax]Phasor value of inner frequency point
Figure FDA0002669445720000041
And
Figure FDA0002669445720000042
wherein
Figure FDA0002669445720000043
And
Figure FDA0002669445720000044
is the n-th node fkVoltage phasor and current phasor of the components, and fmin≤fk≤fmax；fkThe unit is Hz;
s109, selecting a frequency calculation point fjs＝fminCalculating the elements to be calculated at fjsImpedance values of the frequency points;
s110, calculating point f of cyclic change frequencyjs＝fmin+ K Δ f, and step S109 is performed once until fjs＝fmin+KΔf＞fmaxJumping out of the cycle; obtaining the frequency-impedance value of each element to be calculated;
and S111, dividing the alternating-current and direct-current power transmission system into an alternating-current power transmission system part and a direct-current power transmission system part by taking the converter as a boundary, and respectively participating in subsequent harmonic impedance calculation.
7. The system for determining harmonic impedance of a direct current and direct current power transmission system according to claim 6, wherein said elements to be calculated include: the power generation system comprises a generator, a transformer, a power transmission line, a load, a current converter, an alternating current filter and a direct current filter;
the transformer comprises a double-winding transformer and a three-winding transformer;
for the generator, the terminal voltage quantities of the points are calculated using the corresponding frequencies
Figure FDA0002669445720000045
Terminal current phasor
Figure FDA0002669445720000046
Calculating the generator is in fjsImpedance value of frequency point:
Figure FDA0002669445720000047
for a two-winding transformer, the high-side voltage phasor of a point is calculated by using the corresponding frequency
Figure FDA0002669445720000048
And current phasor
Figure FDA0002669445720000049
Low side voltage phasor
Figure FDA00026694457200000410
And current phasor
Figure FDA00026694457200000411
Calculating transformer in fjsImpedance value of frequency point:
Figure FDA00026694457200000412
wherein: k is the actual transformation ratio of the transformer,
Figure FDA00026694457200000413
to the equivalent impedance to the high voltage side of the transformer;
for the three-winding transformer, the same processing mode as BPA is used, namely the three-winding transformer is firstly converted into two double-winding transformers; then, calculating to obtain harmonic impedance values of the two double-winding transformers by utilizing the method for calculating the harmonic impedance of the double-winding transformers;
for the transmission line, the I-side voltage phasor of the point is calculated by using the corresponding frequency
Figure FDA00026694457200000414
And current phasor
Figure FDA00026694457200000415
Voltage phasor at J side
Figure FDA00026694457200000416
And current phasor
Figure FDA00026694457200000417
Calculating the line at fjsImpedance value of frequency point:
Figure FDA0002669445720000051
for the load, calculating the voltage phasor of the load node of the point by using the corresponding frequency
Figure FDA0002669445720000052
And load current phasor
Figure FDA0002669445720000053
Calculation load at fjsImpedance value of frequency point:
Figure FDA0002669445720000054
for the converter, the harmonic impedance calculation is divided into an AC side equivalent impedance and a DC side equivalent impedance:
calculating equivalent impedance of the AC side of the converter: converter power grid side alternating bus voltage phasor using corresponding frequency calculation points
Figure FDA0002669445720000055
And the current phasor input to the inverter
Figure FDA0002669445720000056
Calculating the current converter at fjsEquivalent impedance on the ac side of the frequency point:
Figure FDA0002669445720000057
calculating equivalent impedance of a direct current side of the converter: converter valve side DC bus voltage phasor using corresponding frequency calculation points
Figure FDA0002669445720000058
And the current phasor input to the inverter
Figure FDA0002669445720000059
Calculating the current converter at fjsEquivalent impedance on the direct current side of the frequency point:
Figure FDA00026694457200000510
for the converter transformer, the method for calculating the harmonic impedance is the same as the method for calculating the harmonic impedance of the double-winding transformer;
the harmonic impedance calculation method for the ac filter and the dc filter is the same as the method for calculating the load harmonic impedance described above.
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